1. Field of the Invention
The present invention relates to a method for preparing a resin or a particulate material, and more particularly to a method for preparing a resin or a particulate material such as toner for use in electrophotography, electrostatic recording and electrostatic printing. In addition, the present invention also relates to a toner, a developer including the toner, a toner container containing the toner, and a process cartridge, an image forming method and an image forming apparatus using the developer.
2. Discussion of the Background
Resins such as styrene resins and acrylic resins have a good combination of transparency, rigidity and moldability, and a low cost. Therefore, such resins are broadly used not only for domestic house wares, toys, housing of office automation apparatus, food containers, image projecting screens, magnetic recording media, spacers for LCDs, lighting devices, fillers for columns of analysis devices, carriers of drugs, and resin particles for use in drug delivery systems and bioreactors, but also for binder resins and external additives of image forming materials (such as toners) and coating resins for carriers of two component developers.
In order to control the molecular weight of such resins to impart proper melt viscosity and elasticity to a resin, a chain transfer agent is typically used in the polymerization process. This method has advantages such that the properties and processability of the resultant resins are hardly affected over methods using a lubricant or a plasticizer. However, typical chain transfer agents such as mercaptan type chain transfer agents (e.g., dodecylmercaptan) emit bad smell. Therefore, when a resin in which such a chain transfer agent remains is heated, the chain transfer agent is evaporated, resulting in exudation of bad smell. In particular, this problem is serious when foods wrapped by or contained in a film or a container including such a chain transfer agent are heated in an electronic oven or when a toner including a binder resin including such a chain transfer agent is heated in a fixing process.
In attempting to solve the problem, the following methods have been disclosed:    (1) the added amount of the chain transfer agent is controlled while the polymerization temperature is controlled (for example, published unexamined Japanese patent applications Nos. (hereinafter referred to as JP-As 2001-026619 and 2001-031046);    (2) α-methyl styrene dimmer is used as a chain transfer agent (JP-A 11-292907);    (3) chain transfer agents having a specific molecular structure are used (JP-As 2001-281931, 2002-040711, 2002-091067, 2002-091070 and 2003-330226);    (4) the resultant resins are washed with a washing liquid including a specific material (JP-As 2002-131981-3, 2002-131985, 2002-139863, 2003-098744 and 2003-149861); and    (5) deodorants are used (JP-As 2002-108015 and 2003-098745).
However, the bad smell problem cannot be sufficiently solved by these methods.
Resins are also used for image forming fields such as electrophotographic image forming methods.
Various electrophotographic image forming methods including the methods disclosed in U.S. Pat. No. 2,297,691 and published examined Japanese patent application No. (hereinafter referred to as JP-B) 42-23910 have been proposed.
Electrophotographic image forming methods typically include the following processes:    (1) an electrostatic latent image is formed on an image bearing member (e.g., photoreceptors including a photosensitive material) using various devices such as chargers and imagewise light irradiators (latent image forming process):    (2) the electrostatic latent image is developed using a particulate image forming material (e.g., developers including a toner) to form a visual image on the photoreceptor (developing process);    (3) the visual image is then transferred onto a receiving material such as papers (transfer process);    (4) the visual image is fixed on the receiving material upon application of heat, pressure, combination of heat and pressure and solvent vapor (fixing process); and    (5) image forming particles remaining on the image bearing member even after the transfer process are removed from the image bearing member (cleaning process).
Various methods for forming a toner which serves as a particulate image forming material have been proposed. At the present time, a need exists for a toner preparation method by which a toner can be prepared with low energy without causing environmental pollution. Specifically, melt-kneading/pulverizing methods in which raw materials of a toner are melted and kneaded to be mixed and then the mixture is pulverized have been conventionally used. However, at the present time, polymerization methods (such as suspension methods, emulsification methods and dispersion methods) in which toner particles are formed in a liquid are mainly used. Among these polymerized toners, a capsule toner and a core/shell toner in which a material capable of exhibiting a desired function is microencapsulated or covered with a shell have been proposed in view of environmental protection.
WO97/01131, JP-B 36-10231 and published unexamined Japanese patent application No. (JP-A) 61-228458 have disclosed polymerization methods for preparing a toner having a core/shell structure. Specifically, a method in which resin particles are subjected to an agglomeration treatment or a salting/fusion treatment optionally together with colorant particles to prepare a toner having irregular forms; a method in which a radical-polymerizable monomer in which a colorant is dispersed is dispersed in an aqueous medium, followed by polymerization to prepare toner particles having a desired particle diameter; and a method in which a radical-polymerizable monomer is polymerized in a solvent which can dissolve the monomer but can hardly dissolve (or can swell) the polymer of the monomer, have been disclosed.
It is necessary for each of these toner manufacturing methods to control the molecular weight distribution of the binder resin (i.e., the polymer) to improve the fixability of the resultant toner. In order to prepare a binder resin having a relatively low molecular weight while controlling the molecular weight distribution thereof, a chain transfer agent such as mercaptan compounds such as dodecylmercaptan is used. However, the mercaptan compounds emit a bad smell, and therefore the resultant toner causes a problem in that when toner images are fixed by a heat fixing device, the toner images emit a bad smell.
Toners prepared by a kneading/pulverizing method hardly cause the bad smell problem because the raw materials including a mercaptan compound are heated in the kneading process, resulting in evaporation of the mercaptan compound. However, since toner particles prepared by a polymerization method are not heated after the toner particles are prepared, the mercaptan compound used remains in the toner particles, and thereby the smell problem is caused in the fixing process.
In attempting to solve this bad smell problem, the following methods have been proposed:    (1) a method in which a chain transfer agent having a specific molecular structure is used (disclosed in, for example, JP-As 2001-281931, 2002-040711, 2002-091067, 2002-091070, and 2003-330226);    (2) a method in which the resultant toner particles are washed in a washing liquid including a specific additive (disclosed in, for example, JP-As 2002-131981-3, 2002-131985, 2002-139863, 2003-098744 and 2003-149861); and    (3) a method in which a deodorant is added to the toner particles (disclosed in, for example, JP-A 2002-108015 and 2003-098745).
However, the bad smell problem is not sufficiently solved by these methods.
Because of these reasons, a need exists for an image forming material (a toner) which can produce images having good combination of low temperature fixability, releasability, blocking resistance and high temperature/high humidity durability without causing environmental pollution including the bad smell problem.